The invention relates to an equipment and method for removing deposits created in electrolytic refining from the surface of an electrode, such as a cathode.
In the production of many metals, such as copper, zinc or nickel, one of the principal steps in the manufacturing process is electrolysis, where the metal to be produced is precipitated, by means of electric current conducted to the electrolyte, on the surface of an electrode, i.e. a cathode. Usually a cathode is an object provided with a suspension bar left above the electrolyte surface for suspending the cathode in the electrolytic tank and for connecting it to the circuit, as well as a plate-like element, i.e. a mother plate, to be immersed in the electrolyte, on the surface of which mother plate the metal to be produced is deposited.
In modern industrial plants, the cathode plate is usually made of a different metal than the metal to be produced, and the two vertical edges of the cathode plate, or all three edges immersed in the electrolyte, are provided by electric insulation made of plastic, so that the metal deposited on the cathode plate surface is, at least on its two vertical sides, stripped as two separate plates. Metal production by means of permanent cathodes of the above described type, made of a different metal, is carried out so that the metal to be produced is stripped as plate-like elements from the surfaces of the permanent cathodes, and the permanent cathodes are continuously circulated between the electrolytic tanks and the stripping station. The electric insulation provided at the edges of the permanent cathodes is necessary particularly for detaching and processing the deposited metal.
The operation of the manufacturing process and the production of metal require that the metal to be produced is removed sufficiently often from the surface of the cathode plate. Typically the interval between removals is between one and seven days, and because the removal generally requires massive transfer of material and an interruption in the process, the interval between the removals is attempted to be made as long as possible. Therefore the metal deposits are nowadays usually fairly thick, generally clearly thicker than 5 millimeters.
Because the production volumes in plants producing copper, nickel and zinc are large, there are thousands and tens of thousands of cathode plates in the plants, and even the number of those cathode plates that daily enter the removal step is easily thousands or tens of thousands. Therefore mechanized and automated stripping machines are used for removing the metal to be produced from the surfaces of the permanent cathodes. Further, because the manufacturing expenses of permanent cathodes are high, a maximal extension of their lifetime is extremely important from the point of view of the plant. It is true that the insulation provided at the cathode edges can well be replaced, but also the extension of their lifetime is advantageous from the point of view of the plant. Consequently the most important features of the stripping machine are that the machine does neither damage the permanent cathodes nor the edge insulation thereof, and that the produced metal is reliably detached and that the stripping machine can be made to operate at a high speed.
From the patent U.S. Pat. No. 4,840,710 there is known a method for removing a deposit from the surface of a cathode plate. According to the invention, the deposit is removed from the cathode surface by bending the cathode at one point, for example by means of a hydraulic cylinder, and also by utilizing in the removal process a wedge-like element or blasting with pressurized air. The cathode is supported at its bottom edge and held in a vertical position during the bending operation. It is also known to use mechanical striking tools, such as hammers, in the removal of deposits. However, in addition to disturbing noise, the known methods also have other drawbacks, for example the fact that the whole deposit cannot be removed by one stroke.
The object of the present invention is to realize an improved equipment for removing metal deposits created in electrolytic refining from the surface of the cathode employed as the electrode, so that the strains directed to the cathode itself are avoided, and the stripping process of the deposit is speeded up.